"Felix T." <Fj******@yahoo.comwrites:

I have a class called Interval(type.ObjectType) that is supposed to

mimic closed mathematical intervals. Right now, it has a lot of

methods like this:

def __add__(self,other):

if type(other) in Numerical:

return Interval(self.lower_bound+other, self.upper_bound

+other)

else:

return Interval(self.lower_bound+other.lower_bound,

self.upper_bound+other.upper_bound)

that return new objects of the same type.

The problem is that if this method is called by a subclass like

class HalfOpen(Interval):

#new comparison methods

...

it returns an object with Interval (not HalfOpen) type.

I either have to redefine methods like __add__ so that they return

objects of the right type (even though the logic is the same) or find

some way to redefine Interval's methods so they are more flexible.

Right now, I am looking at:

def __add__(self,other):

if type(other) in Numerical:

return self.__class__(self.lower_bound+other,

self.upper_bound+other)

else:

return self.__class__(self.lower_bound+other.lower_bound,

self.upper_bound+other.upper_bound)

Is there a standard way to do this, or a better one?

You can use type(self) rather than self.__class__

But I wouldn't make HalfOpen descend from Interval as a half-open

interval is not a kind of closed interval. Moreover you should have

Interval(2, 3) + HalfOpen(5, 7) == HalfOpen(7, 10)

Your implementation will yield Interval(7, 10) if I understand

correctly.

I think if I implemented an Interval class I would have it something

like this:

class Interval:

def __init__(self, left, right, closed_left=True, closed_right=True):

...

--

Arnaud